This invention relates to intermediate sleeves for installing piplines by propelling pipes underground as joined together end-to-end, and more particularly to improvements in a sleeve comprising a spigot member and a socket member telescopically fitted together and adapted to be incorporated into an underground pipeline at an intermediate portion thereof. Heretofore it has been practiced to force cast iron pipes, steel pipes or the like directly into earth by a method, which may be termed "propulsion method," for the installation of underground pipelines where there is the necessity of laying the pipeline beneath railways, rivers or roads, or urban areas with heavy traffic where it is impossible to excavate the ground. According to the basic prior art method, a starting pit is first formed in the ground at one end of the pipeline to be installed, and pipes are joined together end-to-end one after another, such that the axially aligned pipe assembly is forced at its rear end into the earth by propelling means, such as hydraulic jacks, provided in the starting pit so as to cause the front end of the pipe assembly to ultimately reach a terminal pit at the other end of the line responsive to progressive lengthening the assembly. However, the propelling capacity of the hydraulic jacks is limited, and the pipe assembly is subjected to an increasing reaction or counterforce with an increase in the overall length of the assembly, with the result that the assembly, when exceeding a certain length, may possibly be buckled or broken down. Thus, there is an inevitable limitation on the length of the pipeline which can be installed only with the use of the propelling means provided in the starting pit.
In order to overcome this drawback, heretofore it has been proposed to incorporate a telescopic intermediate sleeve means into the pipe assembly at an intermediate portion thereof and to propel the pipe assembly in the manner of vermiculation by pushing the rear end of the assembly and extending the intermediate sleeve means alternately in repetition while progressively lengthening the pipe assembly. More specifically, the intermediate sleeve means comprises a spigot member, i.e. basically an inner pipe, and a socket member, i.e., basically an outer pipe, which are telescopically fitted together. At an intermediate portion of the pipe assembly, one of the socket members is joined to the rear end of a pipe, with one of the complemental spigot members joined to the front end of the next pipe. The intermediate sleeve means is telescopically extended or stretched by propelling means, such as hydraulic jacks, provided on the inner surface of the sleeve to thereby advance the front segment of the pipe assembly. Subsequently, the rear segment of the assembly following the sleeve is advanced by propelling means in the starting pit while collapsing or contracting the sleeve. The pipe assembly is advanced in its entirety by repeating this procedure.
However, the propulsion method employing such previously known intermediate sleeves has some drawbacks notwithstanding its outstanding advantages. First, since the intermediate sleeve eventually constitutes part of the pipeline, there is the necessity of sealing the joint between the spigot member and the socket member of the sleeve after the completion of the propulsion. However, this is very difficult and requires much labor to assemble at the intermediate portion of the underground pipeline a mechanical seal. Such prior art sleeves have been of complex structure such as an inner joint comprising a rubber ring, a divided ring and a pushing ring as illustrated at the left side end in FIG. 3 of the accompanying drawings. Moreover, since the spigot member and the socket member are telescopically fitted together, soil or sand is liable to enter the sliding portion between the members, consequently interfering with or preventing a smooth telescoping movement. Although such intermediate sleeves are usually provided with a cover plate extending from the spigot member intended to prevent the ingress of soil or sand, the prior art seal and plate arrangements generally fail to completely seal off the sliding portion against soil or sand during the repetitive telescoping movement, rendering the members no longer smoothly slidable on each other. Another problem of the prior art systems is encountered with the use of jacks which are usually mounted on the inner peripheral surface of the socket member by suitable brackets. With an increase in the diameter of the pipe, jacks of greater weight are used in an increased number, necessitating increasingly cumbersome procedures for the installation and removal of the jacks. In particular, jacks are difficult to mount on and remove from the upper peripheral portion of the socket member. Indeed, extreme difficulties are experienced in following such prior art procedures at an intermediate portion of the underground pipe assembly.